Update Playground link in documentation (#771)

Author: vim-zz

docs/automation-actions.md

@@ -337,7 +337,7 @@ is:
 
     To achieve the exact review behavior you want, use this iterative workflow:
 
-    1. Start with the [Playground](https://app.linearb.io/gitstream/playground)
+    1. Start with the [Playground](https://app.gitstream.cm/playground)
     2. Add specific guidelines e.g., "Do not comment on formatting issues"
     3. Run in the Playground with a reference PR from your repository
     4. Refine guidelines based on the results